News Release

Perceptions of fetal size influence interventions in pregnancy, BU study finds

Peer-Reviewed Publication

Boston University School of Medicine

(BOSTON) - Nearly one-third of women, without a prior cesarean, reported that they were told by their maternity care providers that their babies might be ''quite large," leading to higher rates of medically-induced labor or planned cesarean deliveries that may not be warranted, a new study co-authored by Boston University School of Public Health and Medicine researchers shows. The study in the Maternal and Child Health Journal found that only a fraction (one in five) of the expectant mothers who were told their newborns might be large actually delivered babies with excessive birth weights - a condition known as fetal macrosomia, or a birth weight of more than 8 pounds, 13 ounces.

But those who were told that they had a "suspected large baby" had higher odds of perinatal interventions, regardless of actual fetal size. Women thought to be carrying big babies were nearly five times more likely to ask for cesarean deliveries, twice as likely to try to self-induce labor, and twice as likely to have medical inductions as other women, the study found.

The association between suspecting a large baby and undergoing medical procedures raises questions about how much information clinicians should communicate to women about fetal size. The authors note that a recent review of common formulas for detecting fetal macrosomia found that none reached acceptable detection and false-positive rates. But maternity providers also are under pressure from patients to inform them about all possible complications, the authors noted.

The findings "tap one of the ongoing dilemmas of clinical care: what should patients be told about possible, but perhaps unlikely, risks?" said co-author Eugene Declercq, professor of community health sciences at BUSPH. "In this case, it's even more interesting because a larger baby is typically a healthier baby and at less risk." He noted that while concerns about bigger babies may be growing, the likelihood of a large baby in the U.S. actually has been declining slightly over the past two decades.

Declercq and co-authors examined data from women without a prior cesarean who responded to Listening to Mothers III, a nationally representative survey of women who had given birth between July 2011 and June 2012. The research team estimated the effect of having a suspected large baby (SLB) on the odds of six labor and delivery outcomes.

The average birth weight of SLB babies in the study was about 7 pounds, 11 oz. - compared to the average birth weight of babies not suspected to be large (7 pounds, 1 oz.). The relatively low association between actual macrosomia and clinicians' suspicion of a large fetus "underscores the challenge of determining fetal size prenatally," the authors said.

The research team found that a suspicion of a large baby appeared to influence patient-provider decisions to perform certain perinatal interventions. The study found, for example, that more than one in three mothers with SLBs noted concerns with the baby's size as the reason why their maternity provider induced labor -- the second-most commonly cited reason among cases of medically-induced labor. That finding is important in light of ACOG guidelines and evidence suggesting that such inductions do not reduce neonatal morbidities for SLBs, the authors said.

While the study did not examine whether mothers or clinicians more often made the decision to have a given intervention, the authors said women's "feelings and beliefs" about having a large baby might influence the choice to seek interventions.

Women with SLBs "may feel uncertain, fearful, and anxious about having to deliver a macrosomic infant and seek medical interventions (e.g., cesarean deliveries or pain relief) to avoid anticipated trauma during delivery," the study says. Such women also may attempt to deliver their babies sooner through various non-medical induction techniques.

The authors suggested that "provider and social support may help reduce unnecessary perinatal medical interventions for women who are told their babies might be getting quite large." Specifically, they said, "crisis-oriented and group-based therapies that address fears of childbirth . . . have been shown to help women who request cesareans prepare for normal vaginal deliveries and may be especially relevant for women with SLBs."

The research team said maternity providers should be "aware of the impact of communicating fetal size concerns" on patients' perceptions about the likely course of labor and delivery. They recommend that future studies be done to review policies and practices surrounding clinical management of pregnancies with suspected large babies, "which will hopefully lead to the development of guidelines that ensure that women with SLBs experience care that reflects the best current evidence and standards."


The research team includes: Erika R. Cheng, formerly with Harvard Medical School and now assistant professor at Indiana University School of Medicine; Candice Belanoff, clinical assistant professor of community health sciences at BUSPH; Dr. Ronald Iverson, director of labor and delivery at Boston Medical Center and an assistant professor at the BU School of Medicine; and Dr. Naomi Stotland, assistant professor at the University of California San Francisco School of Medicine.

The study is available here: (

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